Portrait emerging of Las Vegas shooter as man 'descending into madness'

In the months before his deadly rampage, 64-year-old Stephen Paddock was a man "descending into madness," according to a person briefed on new findings in the investigation.

More details are emerging, investigators say, that suggest Paddock's mental state was deteriorating in the weeks before he opened fire into a crowd of concertgoers in Las Vegas on Sunday - significant weight loss, an increasingly slovenly physical appearance and an obsession with his girlfriend's ex-husband.

Authorities were hoping to learn further details about Paddock's final weeks from the gunman's girlfriend, Marilou Danley, who traveled to the Philippines just two weeks before the shooting, arriving in Manila on Sept. 15, according to travel records obtained by ABC News. She flew back to the United States after the shooting, arriving in Los Angeles on Tuesday night, and was met by investigators at the airport.

Danley was questioned by the FBI on Wednesday, and she denied having any knowledge of Stephen Paddock's plans to kill, according to multiple law enforcement officials.

On Wednesday evening, Matthew Lombard, Danley's attorney, delivered a brief statement from his client to reporters.

"He never said anything to me or took any action that I was aware of that I understood in any way to be a warning that something horrible like this was going to happen," she said in the statement.

According to Danley, Paddock told her he had found a cheap last-minute plane ticket to the Philippines so that she could visit her family. While she was there, Paddock wired her a substantial sum of money, which he said she should use to buy a house for her and her family.

"I was grateful but honestly I was worried that first the unexpected trip home and then the money was a way of breaking up with me," she said.

Danley is not in custody and is free to go as she pleases, but investigators have made clear that she remains a person of interest, especially after authorities discovered an additional cache of weapons, ammunition and explosives at the home she shared with Paddock in Mesquite.

"We are continuing the investigation into that female," Sheriff Joseph Lombardo, the chief of the Las Vegas Metropolitan Police Department, said on Monday. "There are several questions that need to be answered."

Through her lawyer, Danley said she intends to fully cooperate with the ongoing investigation.

ABC News' Mark Osborne and freelancer Anna Marie Cerezo contributed to this report.